The present invention relates to a thermoplastic polymeric sheet material used for preventing growth of aquatic weeds.
The presence of some aquatic weeds in waterways can become problematic. For example, the introduction of Eurasian millfoil in Canadian lakes and canals has resulted in clogging of certain sections of these lakes and canals. Uncontrolled aquatic weed growth may also lead to impediment of flow of water through irrigation ditches. Further, in sub-tropical and tropical climates aquatic weeds tend to harbour and provide a food source for water snails. Such water snails can be carriers for parasites and diseases e.g. shistosomiasis which are transmissible to human beings and other animals. It may be seen therefore that methods of controlling or eradicating aquatic weeds in waterways is often desirable.
Herbicides are not often used because of dilution in the water to which they are added. Harvesting e.g. semi-annually tends to be expensive and requires land-based areas set aside for decomposition of the harvested weeds.
It is also known to apply directly over rooted aquatic plants a foraminous screen e.g. closely woven glass fibre screening to control weed growth at the bottom of bodies of water. Such a screen is disclosed in U.S. Pat. No. 4,056,936 to J. R. Mayer issued Nov. 4, 1977. Such foraminous screen material permits some growth of aquatic weeds, but because of the relatively small size of the holes in the screen the thickness of roots or stems which pass therethrough are controlled, thus stunting the growth of such weeds. Stunting of growth of weeds on the bottom of the water body is also aided by the effect of the screening to partially block sunlight from reaching the bottom of the water body. Closely woven screening is not entirely satisfactory, however, because it permits some growth of the weeds. For plants such as Eurasian millfoil which may propagate by suckers, cuttings or seedlings, any control method which permits growth is less desirable than methods which do not permit growth.
Another material for controlling weed growth has now been found.
Accordingly the present invention provides a film, of a thermoplastic synthetic polymer, having a plurality of incisions therein, each incision being shaped to form at least one flap of film adjacent the incision, such film also having a light transmittance in the 200 to 650 nm wavelength range of less than 50%.
In a preferred embodiment each incision is shaped such that the flaps adjacent each incision have an area of between about 1 and about 25 cm.sup.2.
In another embodiment there are between about 36 incisions and 1 incision per square meter of film.
In a further embodiment each incision is in the form of a vee, forming a triangular flap, the area of each such flap being between about 1 and about 25 cm.sup.2.
In yet another embodiment the thermoplastic synthetic polymer is selected from the group consisting of nylon, homopolymers and copolymers of C.sub.2 -C.sub.3 olefins, polyesters and polyvinylchloride.
Nylon films e.g. cast i.e. unoriented nylon 6 and nylon 66 films are preferred because they have densities higher than the density of fresh water and because water has a plasticizing effect on nylon which permits the nylon film to substantially conform to small irregularities on the bed of a waterway. Synthetic thermoplastic polymers which are less dense than fresh water may be used for the film of the present invention, but provision must be made to cause the film to remain on the bed of the water body.
In rocky areas reinforced films may be desirable e.g. a fabric of loosely woven polyethylene tapes, coated with polyethylene having the incisions therein.
In a further embodiment the thermoplastic synthetic polymer contains sufficient opacifying material to impart a light transmittance to the film of less than 50% in the 200 to 650 nanometer wavelength range as measured using a Cary* spectrophotometer with an integrating sphere attachment. FNT *denotes trade mark
In another embodiment the opacifying material, is selected from the group consisting of iron oxide, aluminum, titanium dioxide, calcium carbonate, talc, wollastonite, mica, lead oxide, zinc oxide, chromium oxide, calcium metasilicate, silicon dioxide and carbon black. In a preferred embodiment carbon black is added in the amount of between about 0.2 and about 2.0% by weight of the polymer.
In another embodiment the film has a thickness between about 25 and 250 .mu.m.
In yet another embodiment the thermoplastic synthetic polymer contains sufficient opacifying material to reduce the light transmittance to less than 10% in the 200 to 650 nm wavelength range, and preferably less than 5% in the 200 to 650 nm wavelength range.